There have been known processes for preparing porous (expanded) and non-porous organomineral products by reacting polyisocyanates with aqueous alkali silicate solutions (water glasses); see DE-A-No. 17 21 70 384, DE-A-No. 24 60 834 and EP-P-No. 0 000 579. These processes preferably use alkaline, dissolved water glasses having different solids contents and Me.sub.2 O/SiO.sub.2 ratios. To produce a change in the properties of the water glasses or the products resulting therefrom, most simply, the water glasses are mixed with organic additives that are preferably soluble and can be admixed in liquid state. Examples of additives are hardening substances, such as formamide, glyoxal, stabilizers, such as formaldehyde solutions and elasticizing substances, such as certain epoxide resins and polyethers.
More complicated processes for preparing organomineral products make use of mixtures of water glass solution and preparations containing reactive NCO groups with or without additional modifiers causing the components to undergo a chemical reaction when being mixed. The end products thus obtained can be porous or non-porous. Depending on the formulation (blowing agent), the products obtained are expanded foams with low compression strength or non-expanded organomineral products; see FR-A-No. 1,419,552, U.S. Pat. No. 3,634,3 GB-A-No. 1,445,940 and DE-A-No. 23 59 609.
The products of these processes have been proposed for use in the most different industries as putty, adhesives, insulating material against high or low temperatures and for sound protection, coating and sealing material, for instance against water. While in view of their low price and their special properties as inorganic-organic products, their importance is increasing, their applications are limited, especially those of the non-expanded products, in view of their insufficient mechanical strength. For instance, known non-expanded products, only show insufficient tensile bending strength after 2 hours at 50.degree. C. After 8 days, they still show tensile bending strength values that are lower than the corresponding values of purely organic products.
When taking a closer look at reaction systems consisting of water glass solutions and NCO-group bearing preparations, the difficulties in the formulation will become apparent. On the one hand, the complicated chemical reaction scheme has to be made controllable operation-wise. On the other hand, the end product must meet very specific requirements. Since the requirements are frequently diametrically opposed, the common denominator found is insufficient. So far, these facts have considerably restricted the use of reasonably priced water glass solutions as organic/inorganic systems.
In reaction systems containing a polyisocyanate and an aqueous water glass solution a stoichiometric NCO/OH ratio cannot be achieved so that the reaction proceeds in an uncontrollable manner. Therefore, the polyisocyanate cannot be expected to form in any way an organic polymer structure of any practical use. For this reason, the reaction of polyisocyanate in water glass solutions is of technical interest only in as far as gaseous CO.sub.2 which can be considered as hardener and coagulant for the water glass is released when R--NCO and water react with each other. The low molecular urea product resulting from the polyisocyanate remains distributed in the mineral structure of the water glass as hard filler in the form of very fine particles.
In practical formulation, another problem arises from the excess amount of gaseous CO.sub.2. DE-A-No. 17 70 384, for instance, see page 6, lines 9 to 14, already points out the necessity to observe the stoichiometric ratio of the reactants as much as possible. However, it does not indicate how this is to be achieved.
Moreover, in connection with the stoichiometric ratio, only the R--NCO/OH ratio is considered. No thought is given to the importance of a reaction ratio of Me.sub.2 O/SiO.sub.2 /CO.sub.2 - defined in whatever way. The next aspect pointed out is that with a higher polyisocyanate portion, the reaction proceeds rapidly and also tends to froth up. In view of these facts, the utility of the products obtainable according to said publication is considerably restricted.
From the mold manufacture where molds from sand and sodium water glass are prepared, it is known that an excess amount of gaseous CO.sub.2 used to harden water glass will adversely influence the stability of the molding composition. This is an effect which occurs in a reaction mixture with water glass on account of a high excess amount of polyisocyanate.
In DE-A-No. 24 60 834, a catalyst which is capable of trimerizing polyisocyanate in a manner known per se is added to the reaction mixture water glass/polyisocyanate. However, the process described in said application merely serves to prepare organomineral foams. DE-A-No. 24 60 834 does not give clear teaching as to the amount of catalyst to be used; in the examples using 2,4,6-tris-(dimethylaminomethyl)-phenol as catalyst and polyphenolpolymethylenepolyisocyanate with an NCO-group content of about 28%, said catalyst is used in an amount of about 18 to 36 mmole per mole of NCO groups. In the case of other catalysts or polyisocyanates the ratio is even substantially higher.
It is the primary object of the invention to provide new organomineral products of polyisocyanates and water glass solutions, which products show high mechanical strength.
It is a further object of the invention to provide new organomineral products of polyisocyanates and water glass solutions, which show high mechanical strength, especially tensile bending strength while retaining the broad spectrum of advantageous physical properties of the known organomineral pro- ducts.
It is still another object of the invention to provide new organomineral products which, in addition to the above-mentioned advantageous properties, are inexpensive.
These and other objects and advantages of the invention will become apparent to those skilled in the art from the following description.